Automatic telephone system



May 23, 1933. F. KAHN AUTOMATIC TELEPHONE SYSTEM Filed Feb. 12, 1932 2 Sheets-Sheet l Frederick L. Kal-m F. L KAHN AUTOMATIC TELEPHONE SYSTEM Filed Feb. 12, 1952 2 sheets-sheet 2 May 23, 1933.

Patented May 23, 1933 UNITED STATES PATENT euries FREDERICK L. KAI-IN, 0F CHICAGO, ILLINOIS, ASSIGNOR, yBY1V[ESI\TE ASSIGNMENTS,"

TO ASSOCIATED ELECTRICLLABORATORIES, INC., OF CHICAGO, ILLINOIS, A CORPO- RA'rIoN or DELAWARE Y 1 AUTOMATIC rntnrrronn sYsTnM Application filed February 1.2, 11932. Serial No. 592,451.

em lo in@` laroe ca acit connectors. More` y .e e

specifically, the object is to provide a switching arrangement for a systemv having a capacity of 10,000 lines, wherein. only half as many groups of second selectors and connectors are required to perform the same switching` operations of the well-known automatic telephone systems of 10,000-line capacity.

lt is customary in regular 10,000-line systems to provide a large group of irst selectors, ten. groups ofV second selectors, and one hundred groups of connectors. However, in some 10,000-line systems the number ot groups of connectors have been cut in half by employing large capacity (20D-line) connectors, similar' to the large capacity connector disclosed in the 'lharp applicatiomserial No. 510,680, tiled January 23, 1931, instead ofA the regu-lar (p100-line)V connectors. Vln the present system, alarge group of' iirst selectors and five groups of second selectors are provided. The reduction in the number of groups or second selectors is accomplished` by arranging the trunking between the first. and secon-d selectors so that each group of second selectors is accessible from two diiierent levels ot the-first selector. The level over which the second selector is seized determines the test wiper to be used in selecting a 200-line connector. Since only tive groups of second selectors are required, and each group has ten levels, one for each group of connectors, only litty groups of ZOO-line connectors are required. The test wiper used by the second selector in seizing a connector determines the set of Wipers to be used by the connector to complete a connection.

There are a number of features, not specifically mentioned at this time, relating to various circuit refinements which will be further discussed in connection with the detailed description of the operation of the apparatus shown in the drawings.

The accompanying drawings, comprising Figs. 1 and 2, show by means of the usual cir- .cuit diagrams a sufficient amount of equipment in a telephone system `embodying the invention to permit the same to be readily described andlunderstood. l

lF l's'hows al circuit diagram of a substation A, a lineswitch yand master switch represented by the rectangles LS and MS, respectively, a first selector S1, and a second selector S2, both of which are of the Strowger type. l

Fig.V t2 shows a circuit diagram of a con.l nector H of the Strowger type, and substations B and C. V

-Referring now to Fig-.1, thesubstation Al l tio-n having the usual talking instrumentalities vand a, calling device for' controlling the automatic switches. The line conductors terminate at. the exchange in the individual lineswitch LS (represented by the rectangle), which is one of a plurality of lineswit'ches controlled by' a master switchMS (which is also represented a rectangle). These switches are'similar to those disclosed in Patent No.1,809,086, granted to Voss and Willis June 9, 1931. The iirst selector S1 is mechanically of the usual well-known Strowger vertical and rotary type. The second selector S2' is mechanically of the well-known Strowger vertical and rotary type except that it has two test wipers and two complete sets of associated bank contacts insteadY of the usual single test wiper andr associated bank contacts. Besides the usual relays and magnets,

is an ordinary automatic telephone substal,

thisjswitch has an additional switching relay sides tlie usual relays and magnets, this` switch has an additional switching relay which allows the normallyconnected set of wipers to be used, or switches. to the normallydisconnected set of wipers, depending upon the test wiper used by the second selector seizing the connector. The banks are divided into two units, one for each set of wipers, and each unit has lines extending to subscribers stations in a diderent hundreds group. A subscribers line is shown extending froml the bank contacts accessible to the normallyconnected set of wipers, to substation B, whichis similar to substation A, and to the subscribers individual lineswitch shown), which is similar to lineswitch LS. Another subscribersline is shown extending from the banlr contacts accessible to the normally-disconnected set of wipers, substation C, which is similar to substations A and B, and to the subscribers individual lineswitch (not shown), which isy similar to lineswitch LS. Y

The present system,having been'described in general, will now be described in connection with a detailed description of the operation of the apparatus shown on the drawings. For this-purpose it will be assumed ythat the subscriber at substation A, Fig.V 1, desiresto n converse with the subscriber at substation- B,

Fig. 2. .n

When. the receiver is removed at substationA, a circuit is closed across lineconductors 11 and 12, and the subscribers individual lineswitch LS is operated in the well-known Qmanner andseizes an idle trunk line extending to a first selector. It will be assumed that the lfirst selector S1 is seized by the lineswitch LS, over trunk conductors 133-135.

Y Responsive to the seizure of the first selector S1, the line relay 101 is energized over the following circuit: from battery, upper winding of line relay 101, armature 121 and its resting contact, conductor 133, contact springs 21 and lineswitch LS, line conductor 11, subscribers loop, line conductor 12, lineswitch LS and contact springs 24, conductor 135, armature 125 and its resting contact, lower winding of relay 101, normally closed contacts of overflow springs 130, one side ofv dial tone transformer 1.32, to ground.

When the line relay 101 operates, it opens a point in theV circuit of vertical magnet 105 at armature 109 and its resting contact, and at armature 108 and its front contact it closes al circuit for the upper winding of release relay 102 in series with the lower windings of series relay 103 and release relay 102. More in detail, the circuit closed at armature 108 and its front contact is as follows: from ground, normally-closed contacts 116 of the vertical off-normal springs VON, normally-.-

closed contacts controlled by armature 112, upper winding of release relay 102, armature 108 andits front contact, lower winding of series relay .103, lowerwinding of release relay 102, to battery. The current flow through this circuit is sufficient to operate release relay 102, whose upper winding has a relatively large number of turns,but series vrelay 103 is not operated in this circuit because the lower winding of relay 103 has only a relatively small number of turns. The same is true as regards the lower winding of relay 102.

When relay 102 operates, it opens a point in the circuit of release magnet 107 at armature 110 and its resting contact; places a ground potential on release trunk conductor 134 at armature 113 and its front contact to maintain the lineswitch LS in itsl operated position, and also to maint-ain a ground potential on conductor 13 to maintain the subscribers line busy to all connectors having access thereto disconnects the ground potential for its upper winding at the normally-closed contacts controlled by armature' 112, and by winding of relay 103 is shunted aroun 'the upper winding ot relay 102 and the lower winding oi relay 103. The'closing of this new circuit does not disturb the previously-operated' relay 102, but it results in the strong. magnetization of and the immediate operation of series relay 103, as the upper winding of relay 103 comprises a relatively large number of turns.v When relay 103 operates, it prepares a new circuitior itsown upper winding at armature 117 and its front contact; opens a point in the circuit for the rotary magnet 106 at armature 118 and its resting contact; and at armature 115y and its front contact it prepares a circuit for the' vertical magnet 105.

It'should'be noted that the original energizing circuit forrelay 102 includes ground at the normally-closed 'contacts 116 of the vertical olif-normal springs VON. It sometimes happens that a selec-tor becomes stuck mechanically'and does not restore; conse-l quently the vertical olii-normal springs remain inr an operated position.-4 Due to the way in which the master switch MS tests the bank contacts to' which the releasec'onduc tors, similar to release conductor 136, are connected, it will stop on a trunk vline leading to a selector that is not in normal position, if there is an absence of ground potential/ on the release conductor thereof. lVith the selector in'an oli-normal position it will be seized by a lineswitch such as line-l switch LS. However, when this happens,-

" the release relay 102r does not operate, owing Leifoea conductor 13-1 by armature 113 or" relay 102. ilhen the lineswitch releases, the plunger will align itself with the shaft controlled by the master switch7 due to the fact that it is a se`lt-aligning lineswitch, and will plunge again to seizea newly-selected idle trunk to another selector.

From the foregoing explanation, it is seen that, responsive to the operation of the line relay 101 when the selector i relays 102 and 103 operate successively, and that the selector' is thereby prepared for operation in response to the usual manipulation of the calling` device by the subscriber at substation A. Y

Since tl e circuit of the lower winding of line relay 101 includes the secondary winding of the dial `one transformer 132, dial tone current is transmitted over conductor 135 to the calling subscriber at substation A, and back over conductor 133 and the upper winding oi relay 101 to battery, thereby giving a characteristic signal to tl e calling sul seriber to inform him that he may now start to dial the desired number. f

lrfhen the first digit ot the desired number is dialed. line relay 101 is deenergized momentar-ily number of times, depending upon the value of the dia-lied digit. Each time it momentarily deenergized, line relay 101 a circuit for the vertical magnet 105 armature 109 and its resting contact, whereupon the vertical magnet 105 is operated to raise the shattof the switch, together with the wipers afixed thereto one step. By the operation of' the vertical magnet, the wipers are, therefore, raised step by step until they come to rest opposite the desired lerel of bank contacts. As a further result ot each momentary d-eenergization of the line relay 101. the initial circuit for the upper winding of relay 102 through the lower windings of relays 103 and 102 is opened at armature 10S and its front Contact, and at the normally-closed contact controlled by armature, 103 a short circuit is placed around the upper winding of release relay 102. In

addition, a circuit is completed for the upper winning of relay 103 in series with theV lower winding of relay 102 at the normallyclosed contact controlled by armature 108 over the following circuit: from ground, armature 112 and its front Contact, normallyclosed contact controlled by arma-ture 10S, armature 11?- ann its front contact, contacts 137 of the vertical odi-normal springs VON closed on the first vertical step ofl the switch), armature 111 and its front Contact, upper winding of relay 103, lower winding of reay 102, to battery. Series relay 103 is maintained in its energized position over this circuit. Since lthe lower winding of relay 102 has only a relatively small number of turns.V it cannot remain operated in series with the upper winding of relay 103. However, together with the shunt around the -upper winding and the current fliow through the'lower winding, release relay 102 is held operated between successive impulses.

Each time line relay 101 reoperates lfollowing the delivery of an impulse to the vertical magnet 105, it removes the shunt from around the upper winding of relay 102 at the normally-closed contact controlled by armature 108, whereupon the upper winding ofrelay 102 is again included in a circuit in series with the lower windings of relays 103 and 102 lby the closing of armature 108 and its front contact. In addition, a circuit is now lcompleted for the upper and lower windings of release relay 102 in series with the upper winding of series relay 103 due to the fact that contacts 137 of the vertical ollnormal springs VGN have been closed on the lirst vert-ical step of the switch, over the following` circuit: from ground, armature 112 and its front contact, upper winding of relay 102, armature 11i and its front contact, contact-s 137 of the vertical off-normal springs VGN, armature 111 and its front contact, upn per winding of relay 103, lower winding of rel-ay 102, to battery. 1t should be noted that a circuit is closed for both windings of release relay 102 over two separate paths, one path, including the lower winding of series relay 103, and the other path including the upper winding of series relay 103. Relay 102 is fullyenergized again over this circuit, while the current flowing through the windings of relay 103 in series with the windings of relay 102 is insufhcient to maintain relay 103 operated, but relay 103 remains operated during the receipt of the remaining impulses due to the fact that the current flowing through both its windings makes the relay slow to release.

By way .of an explanation, the first time line relay 101 energizes, release relay 102 also energiZes and causes series relay 103 to energize. The first deenereization of line relay 101, during impulsing, causes the vertical magnet to step the wipers up one step, open ing contacts 116 and closing contacts 137 of the vertical off-normal springs VON. Line relay 101 also places a shunt around the high resistance upper winding of release relay 102, and by the same action it completes a circuit for the high resistance upper winding of seriesrelay 103 in series with the low resistancelower winding of' release relay 102. The shunt around the upper winding and the current flow in the lower winding of relay 102 is just suflicient to keep the relay energized until the line relay is again operated, during impulsing, to again complete the energizing circuit for the release relay 102. Vhen the line relay 101energizes again, after the first deenergization, the high and low resistance windings of release relay 102 are included in the circuit ofthe lower winding of series relay 103 over one path, and the upper winding of series relay 103 in the other path. The amount of current flowing in this circuit is sucient to keep the release relay 102 energized, but the current flowing through both windings of series relay 103 is only sufficient to maintain the relay 103 energized during impulsing.

YWhen line relay 101 comes to rest in an energized condition at tile termination of 'the series of impulses, the series relay 103 subsequently restores to normal, due to the fact that the current flow in both windings of the relay is insuiiicient tomaintain the relay energized, butis sufiicient to make the relay slow to release. Upon restoring, relay 103 disconnects its own upper winding at armature 117 and its front contacts, to prevent the relay from operating until the selector has been released and again seized. The opening of this circuit also opens the path of the energizing circuit of release relay 102, which includes the upper winding of relay 103. However, release relay 102 remains energized over the other path which includes the lower winding of series relay 103. As a further result of the falling back of series relay 103, the circuit to the vertical magnet 105 is ope-ned at armature and its front contact, and at armature 118 and its resting contact it closes a circuit for the self-interrupting rotary magnet 106.

For the purpose of this description it will be assumed that the digitreceived at the first selector is the digit 1, in which case the wipers 12T-129 have been raised one step and are now standing opposite the first level of the bank contacts. y

Therefore, when the `series relay 103 falls back and closes armature 118 and its resting contact, the self-interrupting circuit for the rotary magnet 106 is completed as follows: from ground, armature 113 and its front contact, contacts 119 of the vertical oit-normal springs VON (closed on the first vertical step), armature 114 and its front Contact, armature 118 and its resting contact, contacts 120 of the overflow springs OF, armature 124 and its resting contact, self-interrupting contacts and windings of the rotary magnet 106, to battery.

rlhe automatic rotation'of the wipers 12T- 129, responsive to the buzzer-like action of the rotary magnet 106, continues until an idle trunk is encountered. "When an idle line is encountered (for example, the line coinprising conductors 138, 140, and 141 extending from the first-level bank contact set to the second selector S2), a battery potential is encountered by test wiper 128 by way of test conductor140 and the lower winding of relay 234, completing an operating circuit 'for the upper winding of Vswitching relay 104 to ground at armature 113 and its front contact. Upon energizing, relay 104 opens the circuit of the rotaryv magnet 106 at armature 124 and its resting contact (thereby terminating the rotary movement), and at the same time completing a locking circuit for its lower winding in series with the rotary magnet 106 at armature 124 and its front contacts. Rotary magnet 106 does not operate in series with the lower winding of relay 104 on account of the high resistance of this winding. Relay 104 also opens a point in the circuit for release magnet 107 at armature 122 and its resting cont-act; extends the ground potential on test conductor 134 through to test wiper 128 at armature 123 and its front contact, thereby short circuiting its upper winding; and at armatures 121 and of their respective resting contacts disconnects the incoming conductors 133 and 135 from the windings of the line relay 101 and extends them by way of the front contacts of armatures 121 and 125, wipers 127 and 129, conductors 138 and 141, armatures 221 and 225 and their respective resting contacts, tothe windings of line relay 201 of the second selector S2.

In case selector S1 fails to find an idle trunk line leading to a second selector and continues to rotate until the wipers 127-129 pass beyond the last set of contacts, the contacts 120 and 130 of the overflow spring combinations OF are actuated. Contacts 120 of the overflow spring OF open the self-interrupting circuit to the rotary magnet 106, thereby terminating the rotary movement, while at contacts of the overflow springs OF busy tone current is substituted for dial tone current, giving the calling subscriber a characteristic busy signal. rlhe calling subscriber upon hearing the busy signal replaces his receiver, thereby releasing the partially-established connection.

It has previously been stated that the switching relay104 energized and switched the connection through to the second selector S2, when the test wiper 128 encountered a battery potential. When the test conductor 128 -encountered the bank contact terminating conductor 140, battery was encountered by the test wiper 128 over the following circuit: conductor 140, lower winding of relay 234, contacts 232 of the vertical oH-normal springs VON, resistance 231, to battery. Switching relay 104, of the first selector S1, and relay 234, of the second selector S2, both energize over-.this circuit: The operation of relay 104 has been described in detail hereinbefore. Relay 234, upon operating, prepares a locking circuit for its upper winding atv armature 236 and the front contacts, and at armature 235 and its front contact it connects up the normally disconnected test wiper 229.

It might be well to mention at this time that if the first selector S1 had been operated to the second level, the second selector S2 may be seized as before inasmuch as the line conductors are multipled between bank contacts ofthe first and second levels. It should be noted, however, that the test wiper 128 of the rstselector will encounter the battery ypotential over conductor 139 of the selector S2. When this occurs, the relay 234': is not energized in series with the switch-through relay 10eL of selector S1. Therefore, the normally connected test wiper of the second selector S2 will be used Ain completing aconnection to the connector. y

When the .second selector S2 is seized by the lirst selector S1, over conductors-,138 and 111, line 'relay 201 energizes over the previously-'traced circuit. Responsive to tlie'energization of 'the line relay 201, release relay 202 and series relay 203 successivelyenergize; The 'line relay 201, release relay 202, series relay 203, and switching relay 201 ot the second selector S2, are operated in 'the same manner as has been previously described in connection 'with line relay 101, release relay 102,'series relay 103, and switching relay 104 of the first selector S1. Y

At armature 213 vand its front contact, release relay 202 'completes a locking circuit for relay 231 by way ot armature 236 and its front contact, and by way of the lower winding of lrelay 231 and conductor places a ground on release trunk conductor 1110 to maintain the `switching relay 101 of the selector S1 energized aiter the subsequent release of the line relay 101 and release relay 102. The switching relayl101 is maintained energized overthe lfollowing circuit.: grounded test conductor 140, test wiper 128, arma'- ture 123 and its rontcontact, lower winding of relay 1.01. armature 12% and its iront contact, self-interrupting contacts vand winding ofthe rotary magnet 100, to battery.

lVhen the second digit ef the desired number is dialled by the calling` subscriber, line relay 201 oft the second selector `S2 is dcenergized momentarily a number oi times depending on the value of the digit dialled. Each time it is momentarily deenergized, line relay 201 closes a. circuit torthe vertical magnet 205, whereupon `the vertical magnet 205 is operated to raise the shaft of the switch, together with wipers :227 230, one step. The wipers, .thereforaare raised step-by-step until they come to rest on the `desired level of bank contacts. Vhen the line relay 201 Jomes to rest in an energized condition at `the end of the second series of impulses, the slewto-release l:series relay 203 thereupon falls back. Among other things., the series relay prepares the self-interrupting circuit 'for the rotary magnet v206 at armature 218 and its resting contact. fr

For the pur-pose of this description, it will be assumed that the digit received at the second selector S2 is the fdigit 1, in which case the wipers 227-230, inclusive, have 'been raised one step and are now standing opposite the first level of bank contacts. When Athe series relay 203 falls back and completes the self-interrupting circuit tor the rotary magnet 207 atarmature 218 and its resting contact, therotary magnet 207 -rotates the wipers over the first level of the bank contacts. The circuit for operating the rotary magnet 207 is as follows: ground at armature 213 and its front Contact, contacts 219 of the vertical oil-normal springs VON (closed on the first vertical step of the switch), contacts 220 of the overflow springs OF, armature 2141 and its front contact, armature 218 and its resting contact, armature 224 and its resting contact, self-interrupting contact and winding of the rotary magnet 206, to battery.

The automatic rotation of the wipers, responsive to the'buzZer-like action of the ro tary magnet 207, continues until switching relay 2011 operates upon an idle trunk encountered by tlie test wiper 229. Since vthe test wiper 228 has been disconnected at armature 225 and its resting contact, the test wiper 229 is the wiper that is effective at this time in searching for an idle trunk to a connector. The automatic advancement of the wipers continues until an idle trunk line is reached, whereupon the test wiper229 encounters a battery potential by way of the test conductor similar to test conductor 240, completing an operating circuit for the upper winding of switching relay 204 to ground at armature 213 andits front Contact. lt will be assumed that the connector H, shown in Fig. 2, is .the connector selected by the selector S2. The battery potential encountered by wiper 229 is applied to test conductor 240 by way of armature 339 and its resting contact, contacts 351 of the vertical oil-normal springs VON, resistance element 352, and the battery.

Referring again to theoperation of the switching relay 2041, it will be noted that it opens the circuit oi' the rotary magnet 206 at armature 2211 and its resting contact thereby .terminating the rotary movement) and-at theusalne time it completes a locking circuit for its lower winding .in series with the rotary magnet 200. Due to the high resistance of this winding. the rotary magnet 206 does not operate in series with it. Switching relay 2021 also opens a point in. the circuit of release magnetl 207 at armature 222 and its resting contact; extends the ground potential from armature 213 and its front contact directly to the test wiper 229 by way of armature 223 and its front contact, thereby shunting its upper winding; and, at armatures 221 and 225 and their respective resting contacts, disconnects the incoming conductors 138 and 141 from the windings of 'line relay 201 and eX- tends :them at lthe front contacts of these respect-ive armatures, by way of wipers 227 and 230, conductors 238 and 241, normally closed contacts of armatures 312 and 3,13 to the upper and lower windings of line relay 302 to battery and ground, respectively, of the connector H. Line relay 302 energizes over this circuit.

Responsive to the above-mentioned operation of line relay 302, the release relay 303 of the connector H operates.v At armature 320 and its front contact, the release relay 303 returns ground by of conductor 240, to pro-ride a holding circuit for the preceding apparatus after thev slow-acting release relay 202 of the selector S2 has fallen back,I as will now be explained. y

. Then the line relay 201 is disconnected .at the restingcontacts of armatures 221 and 225, respectively, it opens the circuit including the upper and lower windings ot release relay 202 at armature 203 and its tront contact, and it places a. shunt around the upper winding of relay 202 at the resting contacts controlled by armature 208. The releasing of theline relay does not close a circuit to thevertical magnet 205. due to thetact that the series relay 203 is in its normal deenergized position. Due to the tact that the release relay 202 is made somewhat slow to release, ground. is returned by way ot armature 320 of release relay 303, to hold the selector S2 and preceding switches operated. The circuit for holding the switching relay 204and relay 234 of the'selcctor and the preceding switches operated is follows: ground at armature 320 and its front contact, conductor 240,` test wiper 229, armature 235 and its front contact, armature 223 audits front Contact; one branch ot the circuit in-A cluding the lower winding ot'switching rel ay 204, armature 224, self-interrupting springs and winding of the rotary magnet 206.,.to battery; the other branch includ ing armature 236 and its front contact, upper winding ot relay 234 and battery; the third branch eX- tending ground over test conductorv 140 ot the selector S2 to the preceding switches.

It has been mentioned before that the line relay 302 and the release relay 303 of the connector energize when the switch is seized. Vhen the line relay 302 is operated over conductors 238 and 241, the normal shunt around the upperwinding of release relay 303 is removed, and an energizing circuit is completed for the relay 303 over'the following circuit: ground, upper winding of release Vrelay 303, armature 317 and its front Contact, lower winding ot series relay 304, lower winding of release relay 303, to battery. Release relay 303 energizes over this circuit,

and at armature 322 and its front contact.

closes a circuit for the upper winding oi series relay 304 in series with both-of the windings of release relay 303. However, due to the fact that the high resistance upper winding of release relay 303 is includedin the circuit for the upper winding of series relay 304 over one path and in series with the lower winding of relay 304 over the other'path, the series relay 304 does not energize. In addition, ground potential is connected to conductor 240 at armature 320 and its front con'- tact to hold the preceding switchesvin their operated position, as has been described'. Release relay 303 also opens a point in the circuit for the release magnet 309 at armature 319 and its resting contact, prepares an impulsing circuit for the vertical-and rotary magnets at armature 323 and its front contact, and at armature 321 and its front contact it completes an energizing circuit for the combination ring-cut-oll' and switch-over relay 305 over the following circuit: ground, armature 321 and its front Contact, contacts 327 of the vertical oH-normal springs VON, lower, winding ot relay 305, to battery. Relay 305 energizes over this circuit and prepares a circuit for the vertical magnet at armature 330 and its front contact.

The calling subscriber may now manipulate his calling device in accordance with the third vdigit in the telephone number of the wanted subscriber. When the third digit of the desired number is dialled, relay 302 is deenergized momentarily a number of times depending on the value of the digit dialled. Each time it is momentarily deenergized, line relay 302 closes a circuit for the vertical magnet 310 at armature 318 and its resting contact, whereupon vertical magnet 310 is operated to raise the shaft of the switch, together with the wipers 356-361, inclusive, one step. By the operation of the vertical magnet, the wipers are, therefore, raised step-by-step until they come to rest opposite the desired level of bank contacts. As a further result of each momentary deenergizationol" the line relay 302, the upper winding of release relay 303 is shunted bythe ground at the normally closed contacts-controlled by armature 317, and an operating circuit is completed for the upper winding of relay 304 in series with the lower winding of relay 303. In addition, the circuit through the lower winding of relay 304 and lower winding of relay 303 is opened at armature 317 vand its front contact.v The current flow through the upper winding of relay 304 is sufficient to cause the relay to energize while the current flow through the lower winding of release relay 303 is insutiicient to maintain relay 303 in its energized position. However, together with the shunt around the upper winding ot the relay, it is made slow to release. Therefore, the/release relay 303 remains energized throughout the series of impulses.

Each time line relay 302 reoperates following the delivery of an impulse to the vertical magnet 310, it removes the shunt around the upper winding of release relay 303 and' againv the release relay at armature 317 and its front Contact, which includes both of the windings of the release relay in series with the lower winding of the series relay 304. The current flow through both of the windings of relay 304, each of them in a separate series circuit with the upper and lower windings of rela-y 303, is not suiiicient to maintain the relay 304 in its energized position. However, the relay is made slow to release. Therefore, the series relay 304 will remain in its energized position throughout the series of impulses.

The first momentary deenergization of the line relay 302 completes a circuit for the vertical magnet 310, and the series relay 304 is operated in the manner previously described. Ait armature 326 Vand its front contact relay 304 completes a locking circuit for relay 305. As soon as the vertical magnet raises the wipers of the switch one step, contacts 351 of the vertical off-normal springs VGN open and remore the battery potential from the test conductor 240; contacts 327 of the vertical off-normal springs VON open a point in the nitial energizing Circuit for the relay 305; and cont-acts 324 of the vertical off-normal Springs VON prepare a circuit for the release magnet 300. l

lt will be assumed that the vertical magnet '110 has raised the wipers 356361, inclusive, opposite the bank contactsV shown on the drawings, responsive to the first digit receired at the connector H. lVhen the line rela y 302 comes to rest in itsoperated condition, he Current flow through the series relay 304 is not suiicient to maintain the relay in its energized position, but it does retard the releasing action of the relay. Relay 304 subsequently releases, and at armature 326and 'ts front Contact it opens the locking circuit for relay 305. Relay 305 releases and opens the impulsing circuit for the vertical magnet 310 at armature 330 and its front contact, while at armature 330 and its resting contact `t prepares the impulsing circuit for the rotaryY magnet 311.

The calling subscriber may now transmit the iin al digit of the *anted suliscribes number. The line relay is momentarily deenerd a number of times, thereby causing the series relay 304 to operate in series with the release relay 303 in the manner previously des-ribed in addition, each time the line relay falls back momentarily, it completes a irciiit :or the rotary magnet 311 as follows: ground, armature 313 and i ts resting Contact, armature 323 and its front contact, armature 36 and is resting Contact, armature 345 and its resting contact, armature 330 and its restag Contact, winding of rotary magnet 31.1, to battery. By the operation of the rotary magnet 311, the wipers 356-361, inclusive, are rotated step by step and are finally brought to rest in engagement with the set of bank con- '.acts of the line of sub-station B. It should be noted that the wipers 359-361, inclusive, have also engaged the bank contacts of the line of substation C., However, due to the fact that the wiper switching relay 308 has not been operated, the engagement of the associated bank contacts by these wipers does not have any effect at this time,

1t will be assumed that the called line is busy, when the wipers ofthe connector engage the bank contacts of the called line. Therefore, the two-stepbusy-test relay 306 will b energized in its iirst ste-p over the following circuit: ground by way or" test conductor 363, test wiper 357, armature and its resting contact, normally-closed contacts controlled by armatures 340 and 333, armature 325 and itsfront Contact (relay 304 being slow to release does not fallback immediately after the last impulse has been transmitted to the rotary magnet), armature 341 and its resting Contact, resistance element 335, two-step busy` test relay 306, to battery. Relay 306 energizes in its first step only and prepares a circuit at armature 334 and its front contact A, for energizing itself in its second step. Relay 304 subsequently releases and transfers the ground potential by way of the normallyclosed contacts controlled by armature 325, armature 334 and its front Contact A, winding of the busy-test-relay 306, to battery. The resistance element 335 is disconnected from the circuit-'for relay 306, permittin(r sufficient current to flow through the winding of the relay to allow it to energize in its second step to operate all its armatures. When the busytest relay 306 is operated to its second step, it completes a locking circuit for itself by way of armature 333 and its front contact and the grounded conductor 240; at the same time, it opens its initial energizing circuit by way of test wiper 357 and the grounded test conductor 363; it opens the circuit fer the rotary magnet at armature 336 and its resting conact; at armature 332 and its front contact it connects the busy-tone conductor to one side of the line. The busy-signalling current is transmitted back over the established connec tion to the calling subscriber. The subscriber upon hearing the busy signal, will replace his receiver, whereupon the established connection is released in the manner to be eX- plained hereinafter.

- In the present case, however, it will be assumed that the line kof substation B is idle when the wipers inclusive, come to rest on the terminals of the. called line, in which case the busy relay 306 is not energized Therefore, shortly after the termination of the rotary movement the slow-torelease series relay 304 subsequently falls back and completes the circuit for the slowacting switching relay 30T, follows: grounded test conductor 240, amature and its resting Contact, upper winding of switching relay 307, armature 334 and its resting contact, normally closed contacts of armature 325, normally `closed contacts controlled by armatures 333 and 340, respectively` armature 354 and its resting contact, test wiper 357, thence to battery by way of the bridge-cut-olie winding of the associated lineswitch (not shown), which lineswitch may be the same as the lineswitch LS, associated with the line oi substation A. Responsive to the closure of this circuit, the bridge cutoff of the lineswitch is operated to disconnect the line relay ot the lineswitch from across the line conductors.

ln the connector H, switching relay 307 energizes over the above-traced circuit, and at its lightly-adjusted armature 342 completes a locking circuit for its lower windingfrom ground at armature 321 and its front contact; places a direct ground on test wiper 357 at armature 340 and its front contact; opens the point in the circuit for the rotary magnet at armature 345 and its resting contact; and at armatures 338 and 350 and their respective front contacts connects up the line wipers 356 and 353, whereupon ringing current is projected over the called line to ring the bridged ringer at the substation B. At armature 337 and its front contact, switching relay 307 connects the ring-baclr-tone conductor to the calling` line, to indicate to the calling subscriber that the wanted subscribers line is being signalled. The return path for the ringing current includes the line wipers 356 and the upper winding of the combination switch-over and ring-cut-off relay 305 and ground.

`When the called subscriber at substation B responds to the ringing of his bell by removing his receiver, a direct current bridge is closed across the associated line conductors, whereupon ring-cut-oi relay 305 energizes. Upon energizing, the ring-cut-oti' relay 305 closes a. locking circuit for itself at its lightly-adj usted armature 329; disconnects the line wipers 356 and 358 from its own upper winding and the generator lead at armatures 328 and 331, respectively; opens the ringbacl-tone circuit for the calling subscriber at the normally closed contacts controlled by armature 323; and it completes the talking connection at armatures 328 and 331 and their respective front contacts.

Current is now supplied to the transmitter Vat substation E through the windings of the double-wound back-bridge relay 301, which is accordingly energized. This relay is a reversing relay and has the well-known function of reversing the incoming trunk conductors 233 and 241, as regards their connections with the winding of line relay 302. Relay 301 opens a point in the circuit for the release magnet 309 at armature 350 and its resting contact, and at armature 314 and its front contact it closes an additional holding circuit for the lower winding of switching relay 307.` The reversing of the line conductors 238 and 241 is a standard operation, and is for the purpose of operating a subscribers paystation or metering apparatus, and in some cases is used for supervisory purposes. The desired connection is now completed and the subscriber may converse as desired..

When the conversation is completed, both subscribers replace their receivers. Shoul the calling subscriber restore his receiver lirst, the line relay 302 of the connector H will deenergize and open the circuit of the slow-to-release relay 303. Relay 303 subsequently deenergizes and removes the ground from test conductor 240 at armature 320 and its front Contact, releasing the succeeding switches in the usual manner. The connector H does not release due to the fact that the circuit for the release magnet 309 is opened at armature 315 and its resting contact. The connector cannot be seized by any selector, such as selector S2, because the battery potential is disconnected from the test conductor 2.40 at armature 339 and its resting contact. Armature 339 is held in its operated position by relay307, which in turn is locked up from ground at armature 314 and its front contact.- When the called subscriber hangs up his receiver, relay 301 deenerg'izes, opening the locking circuit for switching relay 307 and completing the circuit for the release magnet 309. Relay 307, upon falling back, opens the circuit for relay 305, which also falls back. When the release magnet 309 is operated, the switch restores to normal in the lusual manner. The battery potential is again applied to conductor 240 as soon as the contacts 351 of the vertical off-normal springs VON are closed when the switch is restored to its normal position. If the called subscriber at substation A hangs up first, the connector H is then vreleased under control of the calling subscriber. It might be well to point out that when the ground is removed from the release trunk conductor 240 to restore the preceding switches, the switch-through relay 204 and the relay 234 of the selector S2 restore to normal. When the switch-through relay 204 releases, a circuit is completed for the release magnet 207, whereupon the switch is restored to normal in the usual manner. The releasing of the lirst selector S1 of the lineswitch LS is performed in the usual manner.

From the foregoing description of the operation of the system, it is evident that the selection of the wiper set in the connector H is automatically controlled over the test wipers in the second selector S2, which in turn are controlled over the test conductor of the level selected by the lirst selector S1. Particular attention should be paid to the arrangement whereby relay 234 of the secl ond selector S2 is operated overl the test conductor 140 when the first selector S1 is dialled to thefirst level and is shunted out when the first selector S1 is operated to the second level. Relay 234 determines which of the two testwipers in the second selector S2 is to be used inV searching for a connector. The connector H is provided withtwo wiper sets, one of which is connected up when relay 308 is operated over test conductor 239 and the other of which is used when the relay 308 is shunted out by theeXtension of a connection over test conductor 240.

It will now be'assumed that a subscriber at substation A desires to establish a connection with the subscriber at substationy C. For the purpose of descriptioinit will be assumed thatk lineswitch LS is operated in ythe usualr manner and'l seizes the first selector S1, as has been described before. When the sub scriber receives the dial tone, he will dial the rst digit of the wanted subscribers number,

which inthiscase is the digit 2.. This will' raise the Wipers 127-129, inclusive, opposite the second level of bank contacts. It will be assumedthat the wipers are then rotated into the bank in the usual manner, and engage the contacts to which the conductors138, 139, .and 141,V extending to the second selector S2, are connected. The battery potential required to operate the switch-through relayv 104 of the first selector is now encountered over conductor 139, contacts 232 of the vertical off-normal springs VON, resistance element 231, to battery. The switch-through relay 104 operatesas before, but in this case through the resistance 231 and-battery direct, instead of operating in. series withV4 relay 234. Ground is returned to hold the first selector S1 operated as soon as the release relay 202 of the second selector S2 is operated responsive vto the energization of the line relay 201.

It will be assumed that the digit dialled to the second.y selector S2 is the same digit dialledinestablishing the previous connection, i. e., the wipers 227-230 hasbeen raised by the operation of the vertical magnet, and are nowstanding on the level corresponding. to the level over which the connector H is accessible. lVhen-the selector S2 automatically rotates to select an idle connector, it will be assumed in this case that the connector H is the one selected. The test wiper 229 may encounter battery over the release trunk conductor 240, but inasmuch as the relay 234 has not been operated to connect up the test Wiper 229at'arn1ature 235 and its front contact, the battery potential encountered by the test Wiper. 229 has no effect atthisV time. Y However, the test wiper 228, whichis the test wiper that is now connected by way of the resting contact of armature 235, encounters a battery potential on test conductor 239. When the battery potential is encounteredby test wiper 228, switchethrough relay 204 of the selector S2 and wiper-switching relay 308 of the connectorH are energized in series over the following circuit: Battery, resistance element 3520i'` the connector H, contacts 351 of the vertical off-normal springs VON, armature 339 and its resting contact, upper winding of wiper-switching relay 308, test conductor 239, test wiper 228, armature 235 and its resting cont-act, upper winding of switchingl relay 204, armature 213 and its front contact, to ground. When the switch-through relay 204 is operated, the line relay of the connector H is energized responsive to the energization of the line relay 302 and completes a locking circuit at armature 321 for the lower Winding of the wiper-switching relay 308. Atarmature 320 and its front contact, relay 303grounds the release trunk conductor 239 by way of the upper winding of wiper-switching relay 308 to hold the switching relay 304, of the selector yS2, energized in series with the rotary magnet 206, in the regular manner. Inr addition, ground is returned over conductor 139 to hold kthe preceding switches operated. v c

The calling subscriber now dials the last two digits of the wanted subscribers number, which are the same as the ones required to establish a connection with the subscriber at substation B. The vertical magnet responds to the impulses dialled and raises the wipers 356-361, inclusive, to the level in which the line of subscribers station-C is terminated. Responsive to the last series of impulses, the 'rotary magnet rotates the wipers into engagement with the bankcontacts terminating conductors 362-367. Due to the fact that the wiper-switching relay has been operated, the lwipers 356-358, inclusive, are disconnected and have no effect at this time. If the wanted subscriber at substationk C is busy at this time, the test wiper 260 will encounter ground potential overv test conductor. 366, therebycausingthe busy-test relay 306 to operate in the manner hereinbefore described. Y

It Willbe assumed, however, that the subscriber at substation@ is not busy when the wipers 359-361 engage the line; therefore, the switch-through relay 307 is energized and locked up over its lower winding. current is Vtransmitted to signal the subscriber at substation C `as before. When the subscriber responds to the. ringing of his bell by removing the receiver, the iingcutoff relay is operated and the talking connection is completed between the vsubscriber at substation A and the subscriber at substation C in the usual manner.v c

The release of the connection is substantially the same as has been previously `described. The only difference in the release of the connection is that the wiper-switching relay 308 is released at the same time that the switch-through relay 307 is released.

Ringing isc It is evident from the foregoing disclosure and description that the level dialled in the first selector determines-the wiper set to be used in the connector to complete aconnection, and also that only half as many groups of second selectors are required due to the fact that each second selector group is accessible over two levels. When the second selector is seized over one level, an auxiliary relay is energized to connect up'a normally disconnected test wiper of the second selector, while if the second selector is seizedover another level, the auxiliary relay is notenergi'zed, and, therefore, the normally connected testV wiper is used.- The test wiper used in the second selector determines whichof the two sets of wipers in the connector will be used to complete the connection to the wanted subscriber.'

lVhat is claimedis:

1. In an automatic telephone system, a switch trainresponsive to the digits of a called number to extend a. connection, said switch train comprising a first switch responsive to a first digit, a second switch responsive to a second digit, and a last switch responsive to the last two digits of said number, a plurality of wiper sets on said last switch, two test wipers and a singleset of line wipers in said second switch, means in said second switch dependent upon the level selected by the first digit for selecting one of said test wipers, and meanszin said last switch dependent upon the 'test wiper used by the second switch in selecting said last switch for selecting one ofsaid wiper sets.

2. In an automatic telephone system, a plurality of serially related switches used in extending a talking connection, a second switch having a set of line wipers and a normally connected and a. normally disconnected test wiper, a first switch, two test conductors each extending from a different level of said first switch to saidsecond switch, means in said second switch for applying a particular potential to said test conductors, means included in the circuit of one of said test conductors for connecting up the normally disconnected test wiper, means in said first switch responsive when said second switch is selected over one of said test conductors for extending the connection from the first to the second switch and for operating the means for connect-ing up the normally disconnected testfwiper in said secondswitch, a last switch having a plurality of wiper sets, and means in said last switch dependent upon the test wiper used by said second switchinselecting said last switch for determining the wiper set over whichsaid connection is to be completed.

3; In an automatic telephone system,-a pluralityA of serially related switches for extending a connection, a first switch having two line wipers and a test wiper, aA trunk line comprising two line and ltwo test conductors extending from said first switch to a second switch, said second switch having two line wipers and a normally connected and a normally disconnected test wiper, a trunk line comprising two line and two test conductorsextendmg from said second switch to a last.

switch, said last' switch having a plurality of wiper sets, means for positioning the wipers of said first switch to select said second switch over said .two line conductors and one of said two test conductors or over said two line conductors and the other of said two test conductors, means in said-second switch dependent upon the test conductor selected by said first switch forfdetermining the'test wiper to be used by-said second switch in selecting said last switch, means for positioning thewipers of said second switch to select said las't switch, and means in said last switch dependent upon the test conductor selected by said second switch for determining the wiper set to be used to complete said connection;

el. In an automatic telephone system, a switch accessible' to other switches over two levels, separate test conductors extending lfrom said other switchesto said switch, a

normally connected and anormally disconnected test wiper and two line wipers, means responsive when said switch is selected over one of said test conductors for connecting up the normally disconnected test wiper, said means non-responsive when said switch is seized over the other of saidtest conductors to permit the normally connectedtest wiper to be used, said line wipers beingused to complete the connection-regardless of the test conductor` used in selecting the switch.y

5. In an automatic telephione system, av

switch-train comprising three switches, the second `switch being accessible to the first switch over two paths, one path comprisingv two line conductors and a first test conductor, the other path comprising a multiple-of said line conductors and alsecond test conductor, a plurality of wiper sets on the third switch, means for controlling said first switch to select said second switch over either of said paths, and meansin said second'switch controlled over the test conductor of the path selected by said first switch for determining the wiper set to be used in said third switch.

6, l In an automatic telephone system, a plurality of serially related switches used'to establish a connection, the first of said switches being accessible over two paths, one of said-paths including ltwo line conductors and a first test conductor, the other of said paths including a multiple of said'line conductors and a'seconol testY conductor, the second of said Aswitches having two wiper sets over which connections are completed and being accessible over a'single path including ioo iso

two line conductors and two test conductors, means for seizing said iirst switch and for operating it. into connective relation with said second switch, and means dependentupon the test conductor used in seizing said lil-st switch for determining the test wiper to be used by said first switch on seizing said second switch. Y

7. in an automatic telephone system, a plurality of serially related switches used to establish a connection, the lirst of said switches being accessible over two paths, one of said paths including two line conductors and a first test conductor, the other of said paths including` a multiple of said line conductors and a second test conductor, the second of said switches having two wiper sets over which connections are completed and being accessible over a single path including two line conductors and two test conductors, means 'for seizing said iirst switch and for operating it into connective relation with said second switch, mea-ns dependent upon the test conductor used in seizing said iirst switch for determining the test wiper to be used by said tirstswitch in seizing said second switch, and means dependent upon the test wiper used in seizing said second switch for selecting the wiper set over which the connection is to be completed.

8. In an automatic switch, four wipers comprising two line wipers and a normally connected and a. normally disconnected test wiper for extending connections to a succeeding switch, four incoming conductors comprising two line conducto-rs and two test conductors, said switch being accessible over one path including said line conductors and oneoi` said test conductors and over another path including said line conductors and the other of said test conductors, means responsive over a particular one of said test conductors for connecting up the normally disconnected test wiper, and means for then controlling said switch to extend a connection to a succeeding switch over said line wipers and the normally disconnected test wiper.

9. In an automatic switch, a plurality of wiper sets over which connections are completed, a four-conductor trunk comprising two line and two test conductors over which said switch is accessible, means in said switch responsive when the switch is seized over a path including said two line conductors and a particular one of said test conductors for selecting one of said wiper sets, said means non-responsive when said switch is seized over a path including said two line conductors and the other one of said test conductors to permit the connection to be completed over the other of said wiper sets.

10. In an automatic switch, two wiper sets over which connections are completed, a fourconductor trunk comprising two line and two test conduct-ors over which said switch is accessible to other switches, means in said switch for applying a potential to said test conductors when said switch is in its normal position, means included in the circuit of one of said test conductors responsive when said switch is seized over a path including said two line conductors and a particular one of said test conductors for selecting one of said wiper sets, means also responsive when said switch is seized for applying a diierent potential to said test conductors for maintaining the seizing switch in its operated position, for maintaining the wiper selecting means operated, and for maintaining said switch busy to all other switches having access thereto.

sol

In witness whereof, I hereunto subscribe my name this 8th day of February, 1932.

FREDERICK L. KAHN. 

